Electrostatic coating apparatus and method for applying a hammer tone finish to an article



July 9, 1968 .1. R. MAUGANS ELECTROSTATIC COATING APPARATUS AND METHODFOR APPLYING A HAMMER TONE FINISH TO AN ARTICLE 2 Sheets-Sheet 1 FiledSept. 23, 1964 IN VENTOR.

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y 9, 1968 J. R. MAUGANS 3,392,043

ELECTROSTATIC COATING APPARATUS AND METHOD FOR APPLYING A HAMMER TONEFINISH TO AN ARTICLE 2 Sheets-Sheet 2 Filed Sept. 23, 1964 INVE/V TORheggwdym y l m] A TTORNEYS ywm I Mi

United States Patent 0 3,392,043 ELECTROSTATEC COATING APPARATUS ANDMETHOD FOR APPLYING A HAMMER TONE FINISH TO AN ARTICLE James R. Maugans,Peru, Ind., assigns: to Ranshurg Electra-Coating Corp., a corporation ofIndiana Filed Sept. 23, 1964, Ser. No. 398,554 11 Claims. (Cl. 117-37)ABSTRACT OF THE DISCLOSURE An electrostatic coating apparatus and methodfor applying a hammertone finish to an article. The article is carriedon a loop conveyor through a coating zone around a rotating discatomizer. An auxiliary electrode adjacent a portion of the periphery ofthe disc alters the electrostatic field conditions so that the paintdischarged into the final portion of the coating zone has a largerparticle size than that discharged into the initial portion of thecoating zone.

This invention is concerned with an apparatus and method for applying ahammer finish to articles, utilizing electrostatic coating techniques.

The hammer finish is one in which the coating, as a paint, is patterned,having the appearance similar to that of a surface tapped with a roundedhead of a ballpeen hammer. A finish of this type aids in hiding surfacedefects of the article, yet is smooth and may be readily cleaned bywiping, in contrast with the wrinkle finish which traps dirt in smallcracks.

In the past, hammer finishes have been applied by either of two methods.In the first, utilizing a two-coat application, the article is sprayedwith the desired paint in which there has been dispersed a smallpercentage of leafing or non-leafing metallic pigment. Then when thepaint is partially set, it is sprayed with droplets of paint thinnerwhich produce localized Wet areas in which metallic pigments can orientto produce the desired pattern. The second method produces a hammerpattern with a one-coat hammer material. The two-coat method has theobvious disadvantage, compared to a one-coat operation, of requiring aduplication of equipment and labor. A one-coat hammer coating materialincludes a component which has an incompatibility with other componentsof the coating so that areas will be formed on the film where thisincompatibility shows itself as the film dries to form the hammerpattern. Great care is required in adjusting the solvent content ofone-coat paints to insure that the deposited film has the correct degreeof wetness to produce a large hammer pattern while achieving asatisfactory film thickness without sagging of the film. This solventadjustment has made the application of one-coat hammer tone finishessomewhat difiicult to control. To aid in overcoming this difiiculty,one-coat hammer finishes normally are applied with air spray deviceswhere the degree of atomization and the rate of film buildup can readilybe controlled.

In the electrostatic application of hammer finishes, the hammercharacteristics have been more difficult to overcome. Because of thefine atomization which is obtained with electrostatic spraying apparatusunder normal operating conditions, the paint arrives at the article tobe coated in a relatively dry condition so that the areas ofincompatibility cannot develop within the coating material and thepigment orientation in these areas is not sufficient to 3,392,043Patented July 9, 1968 produce a marked hammer pattern. The addition ofhigh boiling point solvents does not completely solve the problembecause of the difficulty of obtaining a satisfactory film thicknesswithout the film sagging. Attempting to spray electrostatically underconditions of poor atomization results in poor transfer efiiciencies,poor wrap around deposition, and a poor over-all quality of finish.

This invention is concerned with the utilization of electrostaticcoating apparatus and method in the application of a hammer finish. Animprovement in the uniformity of the hammer design is achieved inaddition to the high quality finish and the coating material savingsassociated with electrostatic coating operations.

One feature of the invention is the provision of an apparauts forapplying a hammer finish to an article, including a source of coatingmaterial connected with an atomizing device, a source of high voltagewhich establishes an electrostatic field between the atomizing deviceand the articles being coated, and a means for varying the size ofcoating material particles. More particularly, a rotating disc atomizeris utilized and in a preferred embodiment of the invention an auxiliaryelectrode is located adjacent at least a portion of the periphery of thedisc atomizer, affecting the electrostatic field gradient over thatportion of the periphery of the disc atomizer to cause variation in thecoating characteristics of the apparatus and thus vary the size of thecoating material particles. The degree of hammer effect may be varied byadjusting one or more of the configurations of the auxiliary electrode,its location with respect to the periphery of atomizing disc, or thevoltage to which the auxiliary electrode is charged.

Another feature of the invention is that the article being coated passesthrough an extended coating zone and the disc distributes coatingmaterial in such a manner that several applications of the material aremade to the article during its passage through the zone. The coatingcharacteristics of the atomizer are atfected so that the size of thecoating material particles is larger over a portion of the extendedcoating zone which portion is also extended enough that the entirearticle surface is exposed to at least one complete application of afull range of particle sizes.

A further feature of the invention is that the electrostatic fieldgradient over a portion of an electrostatic disc atomizer is reducedsufiiciently that poor atomization occurs over this portion of theperiphery of the disc.

Still another feature of the invention is that the auxiliary electrodeextending over a portion of the periphery of the rotating disc atomizeraffects the uniform flow of coating material to atomizing edge in such amanner that large paint particles are formed over a portion of theperiphery of the disc atomizing device.

A further feature of the invention is the method of applying a hammertone coating to an article including the steps of atomizing coatingmaterial, establishing an electrostatic field which etfects the transferof atomized particles of coating material to the article being coated,and affecting an operating condition of the atomizing step to vary thesize of the particle of coating material produced over at least aportion of the coating zone through which the article passes.

Further features and advantages of the invention will be readilyapparent from the following specification and drawings, in which:

FIGURE 1 is a diagrammatic plan view of an apparatus employing theinvention:

FIGURE 2 is an elevation view of the apparatus of FIGURE 1;

FIGURE 3 is a plan view of a disc-type atomizer, embodying theinvention; and

FIGURE 4 is an edge view of the disc of FIGURE 3.

The advantages of electrostatic coating in terms of quality of thefinish and efliciency of the coating material deposition are well knownand will not be discussed here. It is s-ufiicient to note that thepresent invention provides an apparatus and method for achieving auniform improved hammer finish While at the same time enjoying many ofthe other benefits of electrostatic procedures.

Turning now to the drawings, FIGURES 1 and 2 illustrate an electrostaticcoating system utilizing a rotating disc atomizer of the typeillustrated in Simmons Re. 24,602, which may be utilized in the practiceof the present invention. In FIGURE 1 a rotating disc is showndiagrammatically, with the articles to be coated, as panels 11, carriedby a conveyor in a generally annular path 13 around the disc. Coatingmaterial is discharged from the rotating disc 10 around the peripherythereof providing an extended coating zone through which-the panels 11move. As will appear, the disc 10 is maintained at a high DC. potentialwith respect to the articles which are grounded, establishing anelectrostatic field therebetween. The particles atomized on the edge ofthe rotating disc are charged and deposited on the articles to be coatedthrough action of the field. The DC. potential which establishes theelectrostatic field may be, but is not necessarily, well filtered. Thespecific potential figures given represent the average value ofunidirectional potential without regard to the peak value of analternating component which may be present.

In order to coat completely a large article, it may be necessary toprovide a relative movement between the disc and article, as byvertically reciprocating the disc while the articles pass through thecoating zone. FIG- URE 2 illustrates an apparatus in which the disc isreciprocated. The articles 11 are supported by hangers 14 from aconveyor 15 and move in a generally circular path around atomizing disc10. Disc 10 is carried on a shaft 17 which extends from disc drive motor18. Drive shaft 17 extends through a metal tube 20 which depends from aninsulating support 21, passing through a metal sleeve 22 carried by afixed insulating support 23. A high voltage DC. power supply 24 ismounted on insulating member 23 and has one terminal connected to a highvoltage cable 25 which in turn is connected with sleeve 22. The otherterminal is connected to a conductive frame member 26, providing areference or ground for the high voltage.

Coating material is supplied to the upper surface of disc 10 by a pump28, from a paint supply 29, through a fiexi'ble tube 30, whichdischarges the paint at a point near the center of the disc. The coatingmaterial used is selected for the one-coat hammer tone quality.

The entire motor and disc assembly is mounted for verticalreciprocation, the tube 20 sliding in the sleeve 22..An arm 32, pivotedat 33, has a pin 34 at the free end thereof which extends into slot 35of bracket 36, which is a part of the movable disc and motor assembly.Pneumatic piston cylinder device 38 is pivotally mounted on frame member39 and the piston rod 40 thereof is connected at an intermediate pointof arm 32. Compressed air, from a source 42 is connected throughconduits 43 and 44, with the piston and cylinder device 38 to effectreciprocation of the arm 32 and atomizing disc assembly 10. A suitablevalve and control are shown in the aforementioned Simmons Patent Re.24,602, to which reference may be had for further details of themechanism and controls.

The relative speeds of the articles 11 along conveyor 15 and of thereciprocation of atomizing disc 10 are such that the disc will undergoseveral complete cycles of reciprocation during the time required forarticles to pass along the circular path 13 through the coating zone.

In accordance with the invention, it is desired to aifect acharacteristic of the coating apparatus during the period of coating, soas to cause a variation in the size of the particles of coating materialdischarged from the disc over a portion of the periphery of the disc,resulting in a hammer finish. By spraying with fine particles undernormal operating conditions during the first portion of the coatingcycle, a uniform film is obtained with the proper dryness to allow asatisfactory film thickness, and a high quality finish with no sagging.Furthermore, substantially all the paint particles are deposited uponthe articles being coated. Alteration of the operating conditions of theatomizer over a portion of its atomizing zone to increase the paintparticle size being discharged through this portion of the atomizingzone results in a splattering etfect upon the uniform coating because ofthe increased size of the particles and their increased wetness. Theportion of the atomizing zone in which operation is affected ispreferably selected so that the splattering effect takes place as thearticle leaves the extended coating zone. This provides the advantagesof the two-coat method of applying a hammer finish with one coat hammerfinish materials and without the duplication of coating equipment. Theincreased wetness of the larger paint particles as they are deposited isdue to the reduced evaporation of solvents because of the increasedvolume to surface ratio of the particles. This invention renders thecharacter of the resulting hammer pattern subject to control byselecting the size to which the paint particles are increased.

In the embodiment of the invention illustrated herein, the decrease inatomization quality over the selected portion of the periphery of theatomizing device is effected by charged auxiliary electrode locatedclosely adjacent the edge of the atomizing device. The auxiliaryelectrode decreases the electrostatic field gradient at the portion ofthe periphery of the atomizing device and interferes with the uniformflow of paint to the atomizing edge. This results in larger paintparticles over that portion of the atomizing device.

The coating material used may be a commercially available one-coathammer finish. Satisfactory results have also been obtained withmetallic paints.

In the specific embodiment of the invention illustrated in the drawings,an auxiliary electrode, identified generally as 77, is locatedimmediately above and adjacent the edge of a portion of rotating discatomizer 10. Electrode 77 is supported by a conductive arm 78 from thetube 20 and is charged to the same high voltage as the disc. Electrode77 comprises a plate member 79 which extends throughout approximately a90 portion of the periphery of the disc. The outer edge 79a of the plateis located outwardly of the edge of the atomizing disc and between thedisc edge .and the grounded articles 11. The presence of the chargedplate 79 with its edge between the edge of the disc and the groundedarticles substantial- 'ly reduces the electrostatic field gradient atthe edge of the disc. This reduction of the field at the edge of thedisc prevents the coating material from being atomized from the disc atthe same rate at which it is atomized when subjected to the full fieldstrength. The paint which builds up on the surface of the disc duringits passage under the auxiliary electrode is discharged in a narrowpattern of coating material particles larger than the particlesdischarged from the unshielded portion of the disc periphery, as thedisc passes from the auxiliary e1ectrode. These particles are dischargedin a generally tangential direction at the intersection of the peripheryof the disc and the trailing edge 79b of the auxiliary electrode. Anelongated probe 80 is secured to the surface of the auxiliary electrodeand extends outwardly generally parallel with the plane of the disc, inthe direction of discharge of the coating material particles. The endportion 81 of the probe extends downwardly at right angles to the discinto the discharge path of the large particles. The physicalinterference of the probe end with the coating material tends to widenthe spray pattern.

In the specific embodiment of the invention illustrated in the drawings,the auxiliary electrode covers approximately one-fourth of the periphery'of the disc. The auxiliary electrode is located over the lower righthand quadrant of the disc and as viewed in FIGURE 1. Articles to becoated pass from the right upwardly and around the disc, traveling in acounterclockwise direction while the disc itself rotates in a clockwisedirection. Thus, the position of the auxiliary electrode correspondsgenerally with the first portion of the loop through which the articlespass, and its terminal edge 79b is located in a portion of the coatingzone from which the particles ar discharged to the articles as theyleave the coating zone. Thus, during the first portion of the travel ofthe articles through the coating zone, they receive a coating of finelyatomized particles which provide an adequate covering of the surface. Asthe articles pass through the last portion of the coating zone, theypass through a pattern of larger, poorly atomized particles, whichprovide a mottled or hammer effect. The reciprocation of the discatomizer is so coordinated with the travel of the articles along theconveyor that the entire surface of each of the articles is thoroughlyexposed both to the finely atomized spray during the first portion ofthe travel through the coating zone and the poorly atomized coatingmaterial in the last portion of the coating zone.

The size of the poorly atomized particles, and thus the resultingpattern, may be controlled by varying the length or annular extent ofthe auxiliary electrode. The longer the electrode, the more opportunitythe coating material has to build up on the surface of the disc and thelarger the particles, producing a rough hammer pattern. As the angularextent of the auxiliary electrode is reduced, there is less buildup ofcoating material, the particles are smaller and the hammer pattern isfiner. The size and location of the probe may be varied to vary thepattern of discharge of the large poorly atomized particles.

I claim:

1. Apparatus for applying to an article a coating with a hammer finish,comprising: a source of coating material; an atomizing means connectedwith said source for discharging finely divided particles of coatingmaterial therefrom; means for transporting articles through an extendedcoating zone adjacent said atomizing device, from a first portion to asecond portion; circuit means connected with a source of DC. highvoltage establishing an electrostatic field between said atomizingdevice and articles to 'be coated, for moving coating material particlestoward said articles; and means for varying the size of coating materialparticles atomized into said extended coating zone, the particles beinglarger in the second portion than in the first portion.

2. Apparatus for applying to an article a coating with a hammer finish,comprising: a source of coating material; a rotating disc atomizingdevice connected with said source for discharging finely divided coatingmaterial particles therefrom; means for transporting articles to becoated through an extended coating zone, in a generally horizontalplane, and a generally circular path around said disc irom an initialportion to a terminal portion of the zone; circuit means connected witha source of DC. high voltage establishing an electrostatic field betweensaid atomizing device and articles to be coated, for moving coatingmaterial particles toward said article; and an auxiliary electrode meansadjacent the disc portion which discharges coating material into theterminal portion of said zone, for increasing the size of the paintparticles being discharged into said terminal portion of said coatingzone.

3. Apparatus for applying to an article a coating with a hammer finish,comprising: a source of coating material; a rotating disc atomizingdevice connected with said source for discharging finely divided coatingmaterial particles therefirom; means for transporting articles to becoated through an extended coating zone, in a generally horizontalplane, and a generally circular path around said disc from an initialportion to a terminal portion of the zone; circuit means connected witha source of DC. high voltage establishing an electrostatic field betweensaid atomizing device and articles to be coated, for moving coatingmaterial particles toward said article; and an auxiliary electrode meanscomprised of a flat electrode parallel to the atomizing edge of saidrotating disc atomizer and extending beyond said atomizing edge, saidelectrode shielding a portion of the disc periphery for varying the sizeof the paint particles being discharged over another portion of theperiphery adjacent the shielded portion.

4. The apparatus of claim 3, wherein said auxiliary electrode means alsoincludes a rod extending from said flat electrode parallel to the discatomizer in the direction of rotation and terminating in a point whichintersects the spray of paint particles from said atomizing edge.

5. The method of applying a hammer finish to an article, whichcomprises: directing a flow of coating material to an atomizing meanshaving an extended atomizing zone; atomizing coating material from saidmeans; establishing an electrostatic field between said atomizing meansand said article; transporting articles through an extended coating zoneadjacent said atomizing means from a first portion to a second portion;and varying the field gradient over a portion of the atomizing zone tovary the particle size, the gradient in the portion 'of the atomizingzone from which particles are discharged into the second coating zoneportion being less than the gradient in the atomizing zone portion fromwhich particles are discharged into said first coating zone portion.

6. A method of claim '5 wherein the particle size is varied over aportion of said extended coating zone by an auxiliary electrode means.

7. A method of claim 6, wherein said coating material is atomized from arotating disc, and said extended coating zone describes an annular patharound said disc, said auxiliary electrode means being located to varythe paint particle size of the coating material applied to the articleover the terminal portion of said extended coating zone.

8. The method of applying a hammer finish to an article, whichcomprises: directing a flow of coating material to a rotating discatomizer; atomizing coating material from said rotating disc; effectiverelative movement between said atomizing disc and articles to be coated,the articles passing through an extended coating zone describing anannular path around said disc from an initial portion to a terminalportion; effecting reciprocation of said disc in a direction generallyat right angles to the plane of movement of said article; establishingan electrostatic field between said atomizing device and said article;and varying the electrostatic voltage gradient of said field over aportion of the atomizing edge of said rotating disc atomizer to vary thesize of paint particles being discharged, the gradient being higher forthe portion of the disc from which coating material is discharged intothe initial portion of the coating zone than for the disc portion fromwhich coating material is discharged into the terminal portion of thecoating zone.

9. The method of claim 8 wherein said variation of the voltage gradientis accomplished by any auxiliary electrode means.

10. The method of applying a hammer finish to an article whichcomprises: establishing an electrostatic field in a coating zone; movingsaid articles through said zone from a first to a terminal portionthereof; atomizing coating material with a fine particle size into saidfirst portion of said coating zone for deposition of the coating 7 8material particles, affected by said field, on said article toReferences Cited form atnnifornz c ozlitinghtherleong and tthereafteraitomiz UNITED STATES PATENTS mg coa mg ma ena W1 a arger par rc-e size1n 0 sax terminal portion of said coating zone for deposition of 27542267/1956 Juvinau 117*93 I I 5 2,780,565 2/1957 Juvrna-ll 11793.42 thecoating material particles, aifected by said field, 0n

3,147,145 9/1964 Simmons 118624 the article to form a nonuniform coatingthereon, overlying the uniform coating. FOREIGN PATENTS 11. The methodof claim 10 in which said electrostatic 747,543 4/1956 Great Brita-infield' affects the particle size and the field gradient is greater forproducing the fine particle size than for pro- 10 M sistant xamin r.

ducing the larger particle siz ALFRED L. LEAVITT, Primary Examiner.

